The prevalence of obesity among American children is at an all-time high, with over 15% of children currently obese. Child obesity is associated with poorer physical/mental health and social wellbeing as well as increased future risk of obesity and cardiometabolic disease. OBJECTIVES: We will evaluate the potential of state policies that address school breakfast and sweetened beverage availability to improve healthy eating and body weight in elementary and middle school children. We test three hypotheses: 1) State level school breakfast requirements increase availability and consumption of school breakfast and increase intake of nutritious foods;2) State restrictions on sales of sweetened beverages at school lead to lower availability of such beverages at schools, lower total intake of these items, and lower prevalence of obesity among children;3) State-level school policies requiring breakfast and restricting sweetened beverage sales have greater impact on low income and minority children. DESIGN: Our analytic strategy replicates an experimental study design by following children who were and were not exposed to policy changes, depending on their state of residence. Comparing children's weight and consumption in states that implemented a policy during the study with those that did not allows us to assess the effect of the policies. We will use the Early Childhood Longitudinal Study, Kindergarten Class of 1998-99 (ECLS-K), which follows a nationally representative cohort of children from kindergarten into 8th grade. ECLS-K includes substantial numbers of minority and impoverished children. We examine 2 sets of outcomes: children's weight (BMI z-score and obesity) and nutrition (breakfast and sweetened beverage consumption). A significant advantage of the ECLSK is that height and weight are measured by trained assessors. We estimate ordinary least squares regressions, logistic regressions, and fixed effects models, using survey weights to ensure representativeness. Our key explanatory variables are state-level policies, which will be compiled into a comprehensive dataset and merged with the ECLS-K data. We include controls for child, home, neighborhood, and school characteristics. We estimate models by race/ethnicity and poverty status. SIGNIFICANCE: State laws requiring better school nutrition potentially offer a simple, inexpensive strategy for improving nutrition and weight among school-children. Yet the effectiveness of these policies has not been explored. This research contributes to knowledge about weight changes during childhood, progression to obesity, and behavioral and environmental factors that affect these, assessing: 1) The responsiveness of schools to state policy changes;2) The influence of state policies on child weight and nutrition;and 3) Whether students displace their consumption of unhealthy goods to out-of school settings. We will provide empirical evidence on these issues from the largest national longitudinal study measuring weight and height in children. Public Health Relevance: Previous research shows that breakfast and soda consumption are both independently associated with children's weight outcomes, suggesting that interventions focused on these may have long-term benefits for child health. This study will evaluate state policies with high potential to improve healthy eating and body weight among children, measuring the effects of state policies that require schools to offer breakfast and that restrict sales of sweetened beverages at school. This policy evaluation will assist policymakers in making informed decisions about whether more widespread legislation in these areas would promote children's health.